The invention relates to a control device for a DC-to-DC converter and a method for operating a DC-to-DC converter, in particular for the voltage supply of a vehicle electrical system of a hybrid vehicle from a high-voltage network.
The supply of a low-voltage vehicle electrical system by the high-voltage network, which is used to supply the electrical drive of the hybrid vehicle, can be ensured. To this end, a DC-to-DC converter can, for example, be used, which removes energy from the high-voltage network, and the high voltage of the high-voltage network can be converted into a corresponding vehicle electrical system voltage.
If the high-voltage source, for example a traction battery, intermittently or permanently fails, the combustion engine can be used in a hybrid vehicle to supply the high-voltage network. As an alternative, the electrical machine can thereby be operated in generator mode, and the kinetic energy supplied by the combustion engine can be converted into electrical energy. The pulse-controlled inverter connected upstream of the electrical machine can then be operated in a so-called voltage control mode (VCM) in order to alternatively supply the high-voltage network with high voltage.
Because the dynamics of an electrical machine are greater than those of a combustion engine by several orders of magnitude, attention is to be paid during operation that power fluctuations in the low-voltage network are not transmitted to the high-voltage network without damping. There is otherwise the risk that the combustion engine can be stalled as a result of large power surges.
The German patent publication DE 103 215 A1 discloses a method for controlling a vehicle electrical system voltage which is produced by a generator of a combustion engine. To this end, a load response function for controlling voltage as a function of load is used when step changes in load in the vehicle electrical system occur. In the event of drops or additions in load, said load response function prevents excessively high step changes in load from occurring in the generator by means of a voltage rise limitation.